Poly-substance use, treatment completion, and contact with the justice system: a multistate analysis of treatments for substance use disorders between 2010-2019 in Chile

A. González-Santa Cruz1, 2, , J. Ruiz-Tagle Maturana1, 3, , M. Mateo Piñones1, 4, , A. Castillo-Carniglia5,


1 Young Researcher, Millennium Nucleus for the evaluation and analysis of Drug Policies
2 Ph.D. student, School of Public Health, Universidad de Chile
3 Ph.D. student, Programa de Doctorado en Políticas Públicas, Universidad Mayor, Santiago, Chile.
4 Ph.D. student, Griffith University, Australia
5 Director, Millennium Nucleus for the evaluation and analysis of Drug Policies; Associate Professor, Society & Health Research Center

Background

Substance use disorders (SUD) often co-occur with criminality, including violence, arrests, and incarceration\(^{[1; 2; 3]}\). People with polysubstance use (PSU) are considered a high-risk population, as they are associated with mortality, relapse, and contact with the criminal justice system (CJS)\(^{[4; 5; 6]}\). Although completing SUD treatment is linked with better outcomes, including preventing contact with CJS, the role of treatment completion in the link between PSU and contact with CJS is unclear\(^{[7; 8]}\). Studies have found mixed evidence regarding the association between PSU and treatment completion rates\(^{[9; 10; 11; 12]}\). Thus, it is crucial to determine the role of treatment completion in order to improve outcomes in people with PSU. However, analyzing the role of treatment outcomes in people with PSU is challenging, as there is limited research on this population in Latin America, and high-risk populations have often been overlooked\(^{[13; 14; 15]}\). The study contributes to a growing literature on the importance of addressing longitudinal dynamics in specific profiles of SUD patients. Studying the link between PSU, treatment completion, and criminality is crucial for evidence-based strategies to address SUD-related issues. Effective interventions and tailored approaches for people with PSU can mitigate societal and individual harms stemming from SUDs and criminal behavior.

Objectives: We aim to estimate the effects of PSU at baseline (vs. single substance use) on the probabilities of (i) completing baseline drug treatment and (ii) contacting with the criminal justice system after treatment, using multistate survival models at 6 months, 1-, 3- and 5-years follow-ups.

Methods

Design: a retrospective cohort based on the administrative data’s record linkage. Data: Chilean substance use treatment programs and Prosecutor’s Office through a deterministic linkage process. Ethics: We are in the process of an amendment to an existing ethical approval from a study using the same data (by the Griffith University Human Research Ethics Committee GUHREC, GU Ref No: 2022/919).

Variables

Exposure: baseline PSU (using more than one main substance among alcohol and illicit drugs at admission to SUD treatment); Mediator: SUD treatment outcome (complete vs. dropout or spelled by misconduct); Outcome: contact with CJS (committing an offense that led to a condemnatory sentence).

Analytical Plan

The study controlled for various confounding variables listed in Figure 1. Patients were weighted by the inverse probability of PSU (IPWs) based on several predictors. Weights were truncated at the 1st and 99th percentiles to avoid aberrant weights\(^{[16]}\).

We described the cumulative incidence rate (x1,000 person-years) of patients with PSU and no PSU at admission, and incidence rate ratios (IRR) of treatment completion and contact with CJS, with and without weighting for the inverse probabilities of PSU at admission (stset reset_time [pw=inverse_probability_weights] id(id) ... command in Stata).
Covariate balance

Figure 1: Covariate balance

We used the illness-death multistate structure to estimate transitions from admission to treatment outcome, treatment outcome to contact with CJS, and admission to contact with CJS (i.e., without completing treatment) for patients with PSU and no PSU.
Multistate scheme

Figure 2: Multistate scheme

We calculated the Aalen-Johansen estimator for transition probabilities at 6 months, 1, 3 & 5 years using multistate in Stata\(^{[17]}\). Future analyses will focus on mediating effects of treatment outcome and using a time-to-first-event approach\(^{[18; 19; 20]}\). Markdowns & codes are available on https://fondecytacc.github.io/nDP/index_prop_grant23_24.html.

Preliminary Results

  • Before IPWs, patients with PSU (56.4 95%CI: 55.3,57.5) had lower incidence rates of treatment completion vs. patients with no PSU (107.5 95%CI: 104.4,110.5) IRR=0.53 95%CI: 0.51,0.54. However, patients with PSU (90.7 95%CI: 89.4,92.1) had greater rates of contact with the CJS vs. patients with no PSU (54.1 95%CI: 52.3,55.9) IRR=1.68 95%CI: 1.62,1.74.
  • After IPWs, patients with PSU (67.4 95%CI: 65.9,69.0) still had lower rates of treatment completion vs. patients with no PSU (87.0 95%CI: 83.5,90.6) IRR=0.77 95%CI: 0.74,0.8, and patients with PSU (80.3 95%CI: 78.8,81.7) also had greater rates of contact with the CJS vs. patients with no PSU (72.2 95%CI: 69.0,75.5) IRR=1.11 95%CI: 1.06,1.17.
    Table 1: Transition probabilities in states
    Transition Time PSU No PSU
    From admission to contact with CJS 6_mths 2.2 (2.1,2.3) 1.8 (1.7,1.9)
    From admission to contact with CJS 1_yr 7.9 (7.6,8.1) 6.6 (6.4,6.8)
    From admission to contact with CJS 3_yrs 24.4 (24.0,24.7) 20.7 (20.3,21.1)
    From admission to contact with CJS 5_yrs 33.3 (32.8,33.7) 29.5 (29.0,30.0)
    From admission to tr.completion 6_mths 3.1 (2.9,3.2) 4.0 (3.9,4.2)
    From admission to tr.completion 1_yr 14.6 (14.3,14.8) 17.6 (17.3,18.0)
    From admission to tr.completion 3_yrs 23.6 (23.2,23.9) 27.0 (26.6,27.4)
    From admission to tr.completion 5_yrs 21.4 (21.0,21.8) 24.9 (24.4,25.3)
    From tr.completion to contact with CJS 6_mths 3.0 (2.0,4.0) 2.4 (1.3,3.4)
    From tr.completion to contact with CJS 1_yr 8.7 (7.5,9.8) 5.9 (4.8,7.0)
    From tr.completion to contact with CJS 3_yrs 21.1 (20.0,22.3) 16.2 (15.1,17.3)
    From tr.completion to contact with CJS 5_yrs 28.6 (27.4,29.8) 23.0 (21.8,24.2)

Transition probabilities: People with PSU have higher probabilities of contact with the CJS, both post-admission and post-treatment, vs. those without PSU. Similarly, they are less likely to complete treatment. Treatment completers had lower probabilities of CJS contact vs. non-completers after 3 years since admission (Table 1).

Discussion

Treatment completion can reduce the risk of criminal justice involvement, evident at the 3-year point when most users have finished treatment. Further analysis is needed. People with PSU may need enhanced treatment to complete treatments and avoid contact with the CJS.

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Funding sources

  • This work was funded by ANID -Millennium Science Initiative Program- N° NCS2021_003 (Castillo-Carniglia) and N° NCS2021_013 (Calvo); The authors have no conflict of interest to declare